Field of the Invention
The present invention relates to a technology for controlling an image formation condition when an image is formed on a recording material on the basis of a detection result of the recording material detected by using an ultrasonic wave.
Description of the Related Art
Up to now, some image forming apparatuses such as a copier and a printer are provided with an internal sensor configured to determine a type of a recording material. In these apparatuses, the type of the recording material is automatically determined, and a transfer condition (for example, a transfer voltage or a conveyance speed of the recording material at the time of the transfer) and a fixing condition (for example, a fixing temperature or a conveyance speed of the recording material at the time of the fixing) are controlled in accordance with a determination result.
Japanese Patent Laid-Open No. 2013-056771 describes an image forming apparatus provided with an ultrasonic sensor configured to determine a basis weight of a recording material by irradiating the recording material with an ultrasonic wave and receiving an ultrasonic wave attenuated via the recording material. In this image forming apparatus, image formation conditions such as the transfer condition and the fixing condition are controlled in accordance with the basis weight of the recording material determined by the sensor.
In the above-described sensor that uses the ultrasonic wave, the determination result may vary in some cases depending on a surrounding environment (for example, an atmospheric pressure or a temperature) where the sensor is installed. Thus, according to Japanese Patent Laid-Open No. 2013-056771, an environmental correction is performed on the basis of an amplitude value of the ultrasonic wave obtained in a state in which no recording material exists between a transmission unit and a reception unit. In more details, the correction is performed on the reception result of the ultrasonic wave which is received via the recording material on the basis of a ratio of an amplitude value of the ultrasonic wave obtained in advance in a known environment to an amplitude value of the ultrasonic wave obtained in an environment at the time of the determination of the basis weight. With the above-described control, an influence on the determination result caused by the change in the surrounding environment is suppressed.
However, the surrounding environment of the ultrasonic sensor also changes in the middle of continuously forming an image on a plurality of recording materials. When a temperature around the sensor rises, the amplitude value of the received ultrasonic wave changes, and the basis weight of the recording material may be erroneously determined in some cases. As a result, an erroneous image formation condition may be set, and an image quality may be degraded in some cases.